Why did Apple go 64-bit? One iOS, to rule them all

Sometime in the future, iPhones might contain as much memory as a Mac or Windows PC. Apple’s iPad could become the notebook of the future, while versions of the Mac may run iOS as well.

It’s a future that might never come to pass. But leaving those options open might be why Apple chose one of the industry’s 64-bit ARM chips to power the new iPhone 5s.

Apple itself designed the A7 chip within the new iPhone, although the chip’s core was licensed from ARM, whose microprocessor designs power the vast majority of all smartphones today. As it stands now, there’s arguably little reason for Apple to do so.

Moving from 32- to 64-bits increases the addressable memory that a microprocessor can access. According to Kevin Krewell, the senior editor of The Microprocessor Report, the maximum addresable memory for a 32-bit operating system and processor is 4GB. Servers shifted to 64-bit OSes and microprocessors relatively quickly, given that enterprise applications and other high-performance computing problems required data sets that easily went beyond that 4GB limit. At present, however, only the Samsung Galaxy Note 3 approaches that, with 3GB of memory. (Apple hasnt said how much memory the iPhone 5s has.)

Apple itself provides several technical reasons to redesign applications for 64-bit architectures, including minimizing paging as well as cache and buffer misses. But Apple’s argument is predicated upon the shift to OS X 10.7, and assumes a 64-bit environment that could be clogged by processing 32-bit code.

Again, that’s not the case now. “Today, 64-bits adds nothing at all to the mobile experience,” Patrick Moorhead of Moor Insights and Strategy, and a former executive at AMD, said in an email. “It allows you to access more than 4GB of RAM. Today’s phones have 1GB to 2GB of RAM. Tomorrow, as mobile processors are doing more, it will make a difference, just as it did in PCs years ago when AMD introduced the Athlon64.”

But just as Apple bridged the iPad and iPhone with a common OS, so might Apple start thinking about taking that strategy further. So says an executive at one of the companies with insight into Apple’s strategy: ARM, which supplies the underlying processor technology within the A7.

”If you just look generally at the mobile industry, and not any one particular OEM, what you see are two major drivers to go to 64-bit: One is to have an addressable memory space greater than 4GB—and the largest on the market is the Note 3—and the other is the unification of OSes across different form factors,” James Bruce, the lead mobile strategist for ARM, said in an interview. “And what you’re seeing is with all the guys playing in different form factors from smartphones to tablets and other form factors...what they want is one kernel, one set of development tools, and to make it very easy for developers, application providers and OS providers with a minimal enginering development.”

Bruce said that he estimated that Apple would see a performance increase of about 10 percent just by jumping to 64-bits. But cross-platform compatibility still offers a more compelling incentive, he said.

”I think you’ll see a general trend in the industry, that if you’re an OS provider, you don’t want to be doing different OSes, different tools, different kernels for each form factor,” Bruce added. “You want maximum commonality, and obviously the long-term aim of any OS provider is to bring that developer community in, and if they come into your community and they’re developing for multiple form factors, that’s even better.”

Even looking out a year or two, it’s doubtful that apps like Angry Birds, RunKeeper, or Candy Crush Saga would require the horsepower of a 64-bit chip. But if Apple intends to bridge the phone, tablet, and notebook with some sort of low-end iOS device, a 64-bit chip could entice developers eager to capture some additional segment of the market.

Apple could also continue building a common processor architecture across various form factors and use chips like the M7 “motion coprocessor” added to the iPhone 5s, to help differentiate them, industry sources said.

So far, Apple’s future strategy is up for grabs. But there are certain public steps that Apple must take if it chooses a certain road, and it’s certainly worth speculating what the choice of the A7 will mean.